In recent years, a precision press-molding method (also called a mold optics method) draws attention as a method for stably providing a large quantity of optical elements such as an aspherical lens, etc., at a low cost, which optical elements are formed of a high-function glass having properties such as high-refractivity low-dispersion or high-refractivity high-dispersion.
In a precision press-molding method, a low-temperature-softenability optical glass that can be molded at a relatively low temperature is used for reducing the damage to a mold release film provided on a press mold or the molding surface of the mold and for increasing the lifetime of an expensive press mold (for example, see Patent Document 1). As disclosed in JP-A-2002-362938, the above optical glass contains Li2O as a glass component for decreasing the glass transition temperature and the sag temperature thereof.
Meanwhile, when the above glass is used for precision press-molding, an altered layer such as fogging or yellowing is liable to occur on the surface of a precision press-molded product. Since a lens is defective if it has such a fogging or yellowing on a surface, it is required to remove the fogging or yellowing formed on the surface by polishing or the like. However, if it is required to polish the lens surface of a precision press-molded product for removing the fogging or yellowing, the advantage of the precision press-molding method (providing a large quantity of optical elements at a low cost) can be no longer taken.